1. Field of the Invention
The present invention relates to the writing of a frequency modulated electrical signal upon an information bearing video disc surface in the form of successive light reflective and light non-reflective regions.
A reading apparatus is described using a reading light beam moving relative to the successive light reflective and light non-reflective regions to reconstruct the stored frequency modulated signal. The reconstructed frequency modulated signal is demodulated in a discriminator and changed to a form suitable for display on a T.V. monitor.
A novel information storage member is described for use in the writing and reading apparatus. This member includes successive light reflective and light non-reflective regions representing the frequency modulated signal.
Bias control circuitry for achieving duty cycle control in the writing apparatus and an improved form of a Pockels cell driving signal is also described.
2. Description of the Prior Art
U.S. Pat. No. 3,474,457 C. H. Becker discloses an optical recording and reproducing apparatus using a highly focused coherent laser beam to selectively burn away discrete, uniform portions of a film deposited on a carrier member. Information to be recorded is applied to a high frequency oscillator having a high frequency pulse repetition rate which is used to form holes in the carrier member. These holes are of substantially uniform and controlled dimensions of extremely diminutive sizes.
The present invention differs significantly from this technique. One of these differences includes changing the information signal to be recorded into a frequency modulated signal having a carrier frequency and frequency changes in time varying from the carrier frequency, and recording this frequency modulated signal upon an information carrier in the form of successive light reflective and light non-reflective regions of variable length to represent the instantaneous frequency of the frequency modulated signal.
U.S. Pat. No. 3,564,131 to E. D. Herold et al, and U.S. Pat. No. 3,720,784 to D. Mayden et al, disclose a system for producing an actual image comprising a multitude of small discrete holes formed by a laser in a radiation absorbing medium. These teach varying the spacing between the discrete holes and varying the size of the holes, respectively, to represent halftones in storing the actual image.
The present invention does not store an actual image. A typical signal source for use with the present invention is a television camera or a video tape recorder furnishing a recorded signal from a television camera. This signal is commonly called a video signal and it appears as a one volt peak to peak electrical signal in the form of a voltage varying with time format. This video signal is changed to a carrier frequency having frequency changes in time varying about the carrier frequency. This frequency modulated signal is stored on the information bearing surface of a video disc in the form of successive light reflective and light nonreflective regions of varying lengths to represent the instantaneous frequency of the frequency modulated signal.
An improved embodiment of applicant's writing and reading apparatus and disc member are described in a publication entitled "A Review of the MCA Disco-Vision System" published in the July, 1974 Journal of the SMPTE, Volume 83.